Professor Colin Masters, a pathology professor from the University of Melbourne who took part in the research, said that there was a 0.2% risk of contracting the disease from the contaminated product, Lyodura, which is no longer used.

The researchers estimated that fewer than 2500 people were exposed to Lyodura during surgery to the brain or other parts of the body from 1972 until it was taken off the market in 1987.

But given the long incubation time of CJD, it may be that patients don't know they have the disease or did not know that their surgeon used that particular product.

"Over the next 10 years it looks like there will be further cases both here and everywhere else of people who have transplants and we will be monitoring their genetic susceptibility and see if their incubation period is in anyway related to their genotype," he said.

Human spinal tissue

CJD is a rare disease that causes dementia and muscle weakness. It occurs naturally in a small percent of the population that is genetically susceptible to it. But it can also be transmitted by contaminated surgical material derived from autopsies, or treatment with human growth hormone from the pituitary gland.

In these five cases, and in other cases overseas, the disease was associated with surgery using Lyodura.

This is made from human dura mater, a material derived from the outer membrane of the spine of human cadavers. Dura mater is used during surgery to plug holes, for example as a membrane to cover a defect.

The researchers also found that Australians had a much higher risk than the Japanese of contracting CJD from the contaminated product. But they could not say why.

Genetic differences, the chance receipt of a highly contaminated batch of Lyodura, or better case assessment in Australia are possible explanations, the researchers wrote.

"The risk in Australia may not be greater than Japan because the Japanese may have underestimated their risk. This may be what the rest of the world eventually find when they do their analysis worldwide," Masters said.

Although Masters stressed that the risk of contracting CJD via Lyodura was very small, he noted that blood donors have to state whether they have had neurosurgery as a caution against transmitting CJD through the blood.

Blood risk too

In related news, an article in today's British Medical Journal called for steps to prevent further transmission of the variant form of CJD (vCJD) via blood transfusions and blood products.

This is the form of CJD contracted from eating contaminated beef or exposure to contaminated beef products.

Late last year, the UK announced the death of probably the first person in the world to have contracted vCJD via a blood transfusion.